1. Field of the Invention
The present invention relates to field emission displays, and particularly to a carbon nanotube-based field emission display.
2. Description of Related Art
Carbon nanotubes are very small tube-shaped structures having the composition of a graphite sheet rolled into a tube. Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes are electrically conductive along their length, are chemically stable, and can have very small diameters (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that carbon nanotubes can play an important role in field emission display devices.
Referring to FIG. 14, U.S. Pat. No. 6,339,281 discloses a method for making a triode-structure carbon nanotube-based field emission display. The method comprises the steps of:    (1) forming a cathode electrode 2, a gate insulation layer 3 and a gate electrode 4 in sequence on a glass substrate 1;    (2) forming a gate opening (not labeled) in the gate electrode 4;    (3) forming a micro-cavity (not labeled) in the gate insulation layer 3;    (4) forming a separation layer 7 on the gate electrode 4 and forming a base layer 8 and 8′ on the separation layer 7;    (5) forming a catalyst layer 9 and 9′ on the base layer 8 and 8′; and    (6) forming a non-reactive layer 5 on the catalyst layer 9′ outside the micro-cavity; and growing carbon nanotubes 6 on the catalyst layer 9 within the micro-cavity by chemical vapor deposition.
However, in practice, there are the following persistent problems in fabricating carbon nanotube-based field emission displays by chemical vapor deposition:    1. In order to achieve a uniform illuminance, a distance between gate electrodes and carbon nanotubes should be kept uniformly constant over a large display area. However, it is difficult to assure desired uniformity of heights of the carbon nanotubes over a large area by chemical vapor deposition.    2. In order to lower a threshold voltage of the gate electrodes, the distance between the gate electrodes and the carbon nanotubes should be as little as possible. However, it is difficult to precisely control a height of the carbon nanotubes to a micro-scale level by chemical vapor deposition.    3. A carbon nanotube array formed by chemical vapor deposition invariably contains a layer of randomly distributed carbon nanotubes, catalyst particles and tiny amount of amorphous carbon, which impair field emission performance of the carbon nanotube arrays and reduce the field emission display's product life cycle.